Reverted P1 version of Program.java and interpreterex.cp and fixed concat for P2.
Concat for P2 is still a bit wierd because it concats the lists globally so
if list was [1,2,3] and we concat that with [2,3], the result is [1,2,3,2,3] and list will
also be [1,2,3,2,3]. This might not be desired behavior.
Merge branch 'master' of github.com:RedGhost/Drexel-CS550